The present invention relates to an information recording and reproducing apparatus, and in particular, to an information recording and reproducing apparatus which has a magnetic disk and is capable of effecting a high-speed transfer of information.
As a result of development of computer systems, the information recording and reproducing apparatus such as a magnetic disk device has recently come to possess a large storage capacity and a high transfer speed. Magnetic disk devices with a 5.25-inch disk and with a 3.5-inch disk are respectively put to use as an external storage device of a desk-top apparatus such as a personal computer and as an external storage device of a portable apparatus such as a portable computer. Unlike the magnetic disk device used in a large-sized, general-purpose computer system, the magnetic disk device of a small-sized computer system is substantially contained in a housing, namely, comprises a head disk assembly (generally called HDA) including a structure in which a rotating disk, a magnetic head, and a head positioning mechanism are integrally arranged and a peripheral circuit thereof. Consequently, the magnetic disk devices are classified depending on the outer diameter of used disk as an 8-inch, a 51/4-inch, or a 3.5-inch disk device. For each of such disk drive units, a side of the housing thereof is obtained by adding about 10 mm to the outer diameter of the respective disk.
In addition, the storage capacity of the magnetic disk drive has been increasing and the period of time (the average access time) required to position the magnetic head to read data therefrom has been reduced as the storage capacity is increased. For example, in an 8-inch disk drive, an access time is 18 ms to 23 ms for a storage capacity ranging from 170 megabytes to 600 megabytes; in a 51/4-inch disk drive, an access time is 85 ms to 20 ms for a storage capacity ranging from 20 megabytes to 380 megabytes; and in a 3.5-inch disk drive, an access time is 85 ms to 40 ms for a storage capacity ranging from 10 megabytes to 40 megabytes.
However, since the rotational speed of the disk is substantially 3600 rotations per minute (rpm), about 8.3 milliseconds are required as the average latency time.
Incidentally, a period of time required, on average, to read information from a magnetic disk is determined by a sum of the average access time and the average latency time. In the prior art, the average access time which takes a longer period of time as compared with the average latency time is reduced to minimize the average access time. In order to reduce the average access time, there have been adopted a method to decrease the weight of the magnetic head arm which is a movable mass, a method to increase the driving force by use of a large-sized voice coil motor, and a structure in which a plurality of magnetic heads are disposed over a surface of a magnetic disk so as to reduce the movable stroke of the disk and to divide the loads between the inner side and the outer side of the disk. However, the method to decrease the average access time has become increasingly difficult in a technological sense, and the degree of the reduction of the average access time is less than that of the increase of the storage capacity of the magnetic disk device, which as a result prevents the system performance from being improved in a system using the magnetic disk device.
U.S. Pat. No. 4,568,988 describes a 3.5-inch magnetic disk device, which is related to the devices described above.
In the prior-art technology, however, considerations have not been given to a reduction of the period of time required to read information written in a magnetic disk or to write information in a magnetic disk device in a comprehensive sense, which leads to a problem that a long period of time is necessary to record or to reproduce information.